ECDA

Current Attenuation:

Current Attenuation can be performed with various electromagnetic tools including the Pipeline Current Mapper and Precision Pipe Locator for AC attenuation and the Stray Current Mapper for DC attenuation. The pipe is located and depth of cover is determined while simultaneously obtaining current measurement and current direction. All the data is captured and stored into a portable submeter GPS instrument for later download into a computer for data compilation and interpretation.

Some advantages of current attenuation include:

	Measurements can be taken at 50 foot, 100 foot or larger intervals. Does not need to be take every 5 feet to be effective.
	Measurements can be taken over many types of cover including concrete, rocks, pavement and water with no detrimental effect.
	Allows the operator a quick way to determine the overall pipeline coating condition.
	Allows the operator to obtain information very quickly on the electrical CP circuit and whether there are shorts, bonds or other unknown areas of concern.
	Gives the operator a fast and reliable way to narrow down the areas of concern where more detailed and time consuming surveys can be performed.

Alternating Current Voltage Gradient:

An ACVG survey is a very accurate and precise technique for identifying cable breaks, holidays and even the position of anodes. It can be used as a macro and micro tool to pinpoint large to very small holidays in a pipeline section. It will give a readout in dBmV which is used in conjunction with the other surveys to allow the operator to determine the severity class of minor, moderate or severe. It is generally quicker than a DCVG survey.

Some advantages of an ACVG survey include:

	Works in various soil conditions (although ground contact can affect readings).
	More sensitive over pavement than other voltage gradient surveys (must wet down the pavement and may require holes in new oily pavement).
	Less susceptible to existing or stray direct currents.
	Identifying shorted casings.
	High accuracy in locating defects.
	Suitable for complex piping arrangements and in congested city areas.
	Involves no trailing wires.
	Can be used in combination with other techniques.
	Readings are digitally displayed and no side drain is necessary.
	Requires only a single operator.

Direct Current Voltage Gradient:

DCVG is a survey technique used to detect flaws or holidays in buried pipeline coatings. Voltage gradients arise as a result of current pickup or discharge at coating holidays. The DCVG technique can locate large and small anomalies on a coated pipeline and even the position of anodes.

Some advantages of the DCVG technique include:

	High accuracy in locating defects.
	Involves no trailing wires.
	Can be used in combination with other techniques.
	Requires only a single operator.
	Identifying cathodic and anodic conditions (at the time of the survey).
	Identifying shorted casings.
	Suitable for complex piping arrangements and in congested city areas, where a "modest" amount of stray current interference can be expected. (In the case of "heavy" interference the instrumentation may not perform satisfactorily.)

Close-Interval Survey:

A CIS survey is a technique used to designate a voltage potential survey performed on a buried or submerged metallic pipeline in order to obtain valid DC structure-to-electrolyte potential measurements at a regular interval sufficiently small to permit a detailed assessment. CIS may provide a more detailed assessment of CP system performance and operation in accordance with established criteria for CP.

Some advantages of the CIS technique include:

	Assessment extends along the entire length of the pipeline.
	Identifying areas of adequate and inadequate cathodic protection.
	Identifying large coating defects.
	Identifying possible interference areas.
	Identifying shorted casings.
	Simple in principle and widely used.
	Complete pipeline right-of-way can be inspected as part of the walk along the pipeline.

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